Antibodies are natural proteins that the vertebrate immune system forms in response to foreign substances (antigens), primarily for defense against infection. For over a century, antibodies have been induced in animals under artificial conditions and harvested for use in therapy or diagnosis of disease conditions, or for biological research. Each individual antibody producing cell produces a single type of antibody with a chemically defined composition, however, antibodies obtained directly from animal serum in response to antigen inoculation actually comprise an ensemble of non-identical molecules (e.g., polyclonal antibodies) made from an ensemble of individual antibody producing cells.
Some bovine antibodies have unusually long VH CDR3 sequences compared to other vertebrates. For example, about 10% of IgM contains “ultralong” CDR3 sequences, which can be up to 61 amino acids long. These unusual CDR3s often have multiple cysteines. Functional VH genes form through a process called V(D)J recombination, wherein the D-region encodes a significant proportion of CDR3. A unique D-region encoding an ultralong sequence has been identified in cattle. Ultralong CDR3s are partially encoded in the cattle genome, and provide a unique characteristic of their antibody repertoire in comparison to humans. Kaushik et al. (U.S. Pat. Nos. 6,740,747 and 7,196,185) disclose several bovine germline D-gene sequences unique to cattle stated to be useful as probes and a bovine VDJ cassette stated to be useful as a vaccine vector.